1. Field of the Invention
The present invention relates to an insulator such as a suspension type insulator, a long-rod insulator, a station post insulator (SP insulator), a line post insulator (LP insulator), a hollow insulator, or a solid-core insulator.
2. Description of the Background Art
As one form of insulators, there are insulators having hardware joined to at least one side of the insulator body via a cement kneaded product cured body. In the category of the insulators of this form, there are suspension type insulators, long-rod insulators, station post insulators (SP insulators), line post insulators (LP insulators), hollow insulators, solid-core insulators, and others. Typically, the insulator body is formed of an inorganic insulating material such as porcelain or glass. Japanese Examined Patent Application (Kokoku) No. 05-42387/1993 discloses a suspension type insulator which is a typical example of the insulators of this form.
The suspension type insulator includes a porcelain body, a metal cap joined to one side of the porcelain body via a cement mortar cured body, and a metal pin joined to the other side of said porcelain body via a cement mortar cured body. Generally, a Portland cement mortar is used in the cured body of the suspension type insulator. The Portland cement mortar is a cement kneaded product obtained by kneading a Portland cement, a water reducing agent, an aggregate, and water, and this is cured to form the cement mortar cured body. The cement mortar cured body in this state firmly joins the metal cap and the metal pin onto the porcelain body.
Further, in other insulators or hollow insulators of this form, a base hardware and a metal flange are adopted as hardware in place of the metal cap and the metal pin; however, in the case of assemblage by joining the base hardware and the metal flange onto one side or onto both sides of the insulator body or the hollow insulator body, a cement mortar cured body of Portland cement is used for joining the base hardware and the metal flange.
In the meantime, in the insulators of this form, high mechanical strength (tensile strength and others) and high electrical strength (dielectric breakdown strength and others) are required in view of the uses thereof, and also it is required that the high mechanical strength and the high electrical strength are maintained for a long period of time. For this reason, the cement mortar cured body requires a high mechanical strength of its own both initially and over a long period of time. In order to meet these requirements, it is optimal to use a cement that can form a cured body having a high strength as the cement constituting the cement mortar cured body.
For this reason, as a cement for forming the cement mortar cured body of an insulator of this type and form, it is desirable to adopt an alumina cement that can exhibit a high strength, as compared with a Portland cement, in place of the Portland cement that is currently used. Further, as compared with the Portland cement, the alumina cement has a small degree of shrinkage as a cement mortar cured body with small variation in the mechanical strength, thereby being advantageous in terms of strength, and also requires a short curing time for curing the cement mortar, thereby being advantageous in this respect as well.
However, since the alumina cement mortar shows dilatant flow properties, a difficulty is involved in the assemblage work for assembling the insulator by injecting the alumina cement mortar into a gap between the insulator body such as a porcelain body and a hardware such as a metal cap or a metal pin. Particularly, in the case of adopting means for allowing porcelain sands to adhere to the joining site of the insulator body, there arises a problem such that the assemblage work is made more difficult.
Therefore, an object of the present invention is to enable the adoption of alumina cement as a cement constituting the cement mortar cured body of an insulator of this type and form, so as to provide an insulator having a high mechanical strength and a high electrical strength and being capable of maintaining the high mechanical strength and the high electrical strength for a long period of time, and further to shorten the curing time in forming the cement mortar cured body to thereby reduce the cost of producing the insulator.
The present invention relates to insulators, particularly to suspension type insulators, long-rod insulators, station post insulators (SP insulators), line post insulators (LP insulators), hollow insulators, solid-core insulators, and others as objects of application.
Therefore, in the present invention, these insulators and hollow insulators are generally referred to as insulators; the dielectric bodies constituting these insulators and hollow insulators are generally referred to as insulator bodies; and the metal caps, metal pins, base hardware, and metal flanges constituting these insulators and hollow insulators are generally referred to as hardware.
Now, the first insulator according to the present invention is an insulator comprising an insulator body and a hardware joined to at least one side of the insulator body via a cement kneaded product cured body, characterized in that the cement kneaded product cured body is a cured body formed by curing a cement paste that is obtained by kneading an alumina cement having a specific surface area of at least 3500 cm2/g and having an amorphous phase of at least 10 nm thickness on an outer peripheral surface of particles, a water reducing agent, and water, said cement paste being cured in a wet state and at a temperature of 40xc2x0 C. or higher.
The second insulator according to the present invention is an insulator comprising an insulator body and a hardware joined to at least one side of the insulator body via a cement kneaded product cured body, characterized in that the cement kneaded product cured body is a cured body formed by curing a cement mortar that is obtained by kneading an alumina cement having a specific surface area of at least 3500 cm2/g and having an amorphous phase of at least 10 nm thickness on an outer peripheral surface of particles, a water reducing agent, an aggregate, and water, the cement mortar being cured in a wet state and at a temperature of 40xc2x0 C. or higher.
The first insulator and the second insulator according to the present invention belong to the first category which is one and the same category having the same principal construction with each other. In both of these insulators, the specific surface area of said alumina cement can be set within a range from 3500 cm2/g to 5000 cm2/g, and the thickness of the amorphous phase that the particles of said alumina cement has can be set within a range from 10 nm to 103 nm. The thickness of the amorphous phase can be adjusted by a length of time for leaving the ground alumina cement to stand. Here, the length of time for leaving the alumina cement to stand represents the period of time in which the ground alumina cement is left to stand before being kneaded with water.
The third insulator according to the present invention is an insulator comprising an insulator body and a hardware joined to at least one side of the insulator body via a cement kneaded product cured body, characterized in that the cement kneaded product cured body is a cured body formed by curing a cement paste that is obtained by kneading an alumina cement having a specific surface area of at least 3500 cm2/g, a polymer-steric-hindrance type water reducing agent, and water, the cement paste being cured in a wet state and at a temperature of 40xc2x0 C. or higher.
The fourth insulator according to the present invention is an insulator comprising an insulator body and a hardware joined to at least one side of the insulator body via a cement kneaded product cured body, characterized in that the cement kneaded product cured body is a cured body formed by curing a cement mortar that is obtained by kneading an alumina cement having a specific surface area of at least 3500 cm2/g, a polymer-steric-hindrance type water reducing agent, an aggregate, and water, the cement mortar being cured in a wet state and at a temperature of 40xc2x0 C. or higher.
The third insulator and the fourth insulator according to the present invention belong to a second category which is one and the same category having the same principal construction with each other. In both of these insulators, a comb-shaped polymer of polycarboxylate series or an aminosulfonate polymer can be adopted as said polymer-steric-hindrance type water reducing agent.
In the first insulator and the third insulator according to the present invention, the mixing ratio of components of the cement paste constituting the cement kneaded product cured body can be set in such a manner that the water reducing agent is 5 wt % or less and the water is within a range from 15 wt % to 30 wt % with respect to the alumina cement.
In the second insulator and the fourth insulator according to the present invention, the mixing ratio of components of the cement mortar constituting the cement kneaded product cured body can be set in such a manner that the water reducing agent is 5 wt % or less, the aggregate is 100 wt % or less, and the water is within a range from 15 wt % to 30 wt % with respect to the alumina cement.
In the first insulator to the fourth insulator according to the present invention, one can adopt an alumina cement having a composition containing Al2O3 within a range from 45 wt % to 60 wt %, CaO within a range from 30 wt % to 40 wt %, SiO2 of 10 wt % or less, and Fe2O3 of 5 wt % or less, as said alumina cement.
In the first insulator and the second insulator belonging to the first category according to the present invention, an alumina cement having a specific surface area of at least 3500 cm2/g and having an amorphous phase of at least 10 nm thickness on an outer peripheral surface of alumina cement particles is adopted as a cement for forming a cement paste or cement mortar constituting a cement kneaded product cured body that joins a hardware to at least one side of an insulator body; and the prepared cement paste or cement mortar is cured in a wet state and at a temperature of 40xc2x0 C. or higher to form the cement kneaded product cured body.
In the third insulator and the fourth insulator belonging to the second category according to the present invention, an alumina cement having a specific surface area of at least 3500 cm2/g is adopted as a cement for forming a cement paste or cement mortar constituting a cement kneaded product cured body that joins a hardware to at least one side of an insulator body; a polymer-steric-hindrance type water reducing agent is adopted as a water reducing agent; and the prepared cement paste or cement mortar is cured in a wet state and at a temperature of 40xc2x0 C. or higher to form the cement kneaded product cured body.
Although the alumina cement paste or alumina cement mortar contains alumina cement as a base, the cement paste or cement mortar used for the work of assembling each insulator belonging to the first category according to the present invention has smaller dilatant flow properties due to the defined properties of the alumina cement, so that the cement paste or cement mortar can be injected more smoothly into a gap between the insulator body and the hardware at the time of the work of assembling the insulator, thereby facilitating the work of assembling the insulator.
In other words, use of alumina cement paste and alumina cement mortar is enabled for the work of assembling the insulator. Particularly, in the case of adopting means for allowing porcelain sands to adhere to the joining site of the insulator body, adoption of alumina cement paste and alumina cement mortar is enabled for the work of assembling the insulator which assemblage work was more difficult. Further, the constructed cement kneaded product cured body has the desired high mechanical strength and high electrical strength due to the alumina cement, and also these strengths can be maintained over a long period of time.
Thus, in the first insulator and the second insulator belonging to the first category according to the present invention, the good flow properties of the cement paste or cement mortar used for the work of assembling the insulators improves the close adhesion to the insulator body and to the hardware and, in synergism with the action of the alumina cement, contributes also to the improvement of the mechanical strength and the electrical strength as an insulator.
Therefore, in each insulator belonging to the first category according to the present invention, the cement kneaded product cured body that functions to join a hardware to an insulator body has a high strength both at an initial stage and over a long period of time due to the alumina cement, so that the cement kneaded product cured body has a high mechanical strength and a high electrical strength, and the high mechanical strength and the high electrical strength can be maintained for a long period of time. Further, since the alumina cement paste and the alumina cement mortar are cured in a short period of time, the cost of producing the insulators can be reduced due to the decrease of the curing time.
Further, although the alumina cement paste or alumina cement mortar contains alumina cement as a base, the cement paste or cement mortar used for the work of assembling the third insulator and the fourth insulator belonging to the second category according to the present invention has smaller dilatant flow properties due to the defined properties of the alumina cement and the water reducing agent, so that the cement paste or cement mortar can be injected more smoothly into a gap between the insulator body and the hardware at the time of the work of assembling the insulator, thereby facilitating the work of assembling the insulator. For this reason, the insulators belonging to the second category according to the present invention produce the same actions and effects as the insulators belonging to the first category.
The mixing ratio of the components of the alumina cement paste constituting the cement kneaded product cured body that exhibits such excellent functions is preferably such that the water reducing agent is 5 wt % or less and the water is within the range from 15 wt % to 30 wt % with respect to the alumina cement. The mixing ratio of the components of the alumina cement mortar adopted for constructing the cement kneaded product cured body is preferably such that the water reducing agent is 5 wt % or less, the aggregate is 100 wt % or less, and the water is within the range from 15 wt % to 30 wt % with respect to the alumina cement.
Further, the alumina cement adopted in these alumina cement paste and alumina cement mortar preferably has a composition containing Al2O3 within a range from 45 wt % to 60 wt %, CaO within a range from 30 wt % to 40 wt %, SiO2 of 10 wt % or less, and Fe2O3 of 5 wt % or less.
The Al2O3 value and the CaO value of the alumina cement are preferably such that Al2O3 is within the range from 45 wt % to 60 wt % and CaO is within the range from 30 wt % to 40 wt % in view of the setting properties of the cement paste and the cement mortar, the mechanical properties of the cured products of these, and their costs. Further, the SiO2 value and the Fe2O3 value of the alumina cement are preferably such that SiO2 is 10 wt % or less and Fe2O3 is 5 wt % or less because, if these are contained in a large amount, these cause retarded setting and decrease in the mechanical strength.
The water in the alumina cement paste and the alumina cement mortar is preferably within the range from 15 wt % to 30 wt % because, the less the water is, the poorer the workability of assembling the insulators will be, though the mechanical strength of the cured product will be improved. The aggregate in the alumina cement mortar is preferably 100 wt % or less because a large amount of aggregate will deteriorate the flow properties of the cement mortar and gives adverse effects on the workability of assembling the insulators, though the aggregate contributes to the improvement of the mechanical strength of the cured product.
Regarding the water reducing agent, there are polymer-steric-hindrance type water reducing agents, electrostatic repulsion type water reducing agents, and others.
In particular, in the third insulator and the fourth insulator belonging to the second category according to the present invention, a polymer-steric-hindrance type is adopted as the water reducing agent. The polymer-steric-hindrance type water reducing agent subjectively exhibits the dispersion action of polymer-steric-hindrance types, such as comb-shaped polymers of polycarboxylate series and aminosulfonate polymers, where comb-shaped polymers of polycarboxylate series are more preferable.
Such a polymer-steric-hindrance type water reducing agent, when adsorbed onto alumina cement particles, extends the side chains such as polyether chains to surround the alumina cement particles to form a steric hindrance, thereby showing a high dispersion and a high fluidity. The longer the side chains are, the larger this effect is. Further, such a polymer-steric-hindrance type water reducing agent has a characteristic such that retarded setting is less liable to occur. The amount of the polymer-steric-hindrance type water reducing agent used is 5 wt % or less, and addition of the polymer-steric-hindrance type water reducing agent exceeding 5 wt % will not produce an effect larger than that.
Thus, in the third insulator and the fourth insulator belonging to the second category according to the present invention, a polymer-steric-hindrance type water reducing agent is adopted as the water reducing agent. In contrast, in the first insulator and the second insulator belonging to the first category according to the present invention, assuming that a conventionally used ordinary water reducing agent can also be used as the water reducing agent, the thickness of the amorphous phase that the alumina cement particles have on the outer peripheral surface is specified to 10 nm or more in addition to specifying the specific surface area of the alumina cement.
This improves the flow properties of the cement paste and the cement mortar and improves the strength of the cement kneaded product cured body. The reason why these effects are produced seems to be as follows.
Alumina cement has a high surface activity immediately after being ground. For this reason, in the case of preparing a cement paste or cement mortar using an alumina cement having a high surface activity immediately after being ground, the hydration reaction of alumina cement with water proceeds rapidly at the time of kneading. As a result of this, it seems that the elution of calcium ions, aluminum ions, and others increases rapidly in the cement paste or cement mortar, whereby the viscosity of the cement paste or cement mortar increases to reduce the flow value, and the assemblage workability is deteriorated.
Further, if the hydration reaction of alumina cement with water proceeds rapidly, pores and defects are generated in the cement kneaded product, thereby decreasing the density. It seems that, because of this, the cement cured body will have a decreased strength, and a decrease in the tensile strength of the insulator will be invited.
On the other hand, when the alumina cement is left to stand immediately after being ground, for example, in air, the moisture in the air is adsorbed onto the outer peripheral surface of the alumina cement particles to produce an amorphous phase on the outer peripheral surface of the alumina cement particles, thereby decreasing the surface activity of the alumina cement. It seems that production of the amorphous phase restrains the elution of ions from the alumina cement, and the shape of the alumina cement particles is improved to a rounded shape to decrease the viscosity of the cement paste or cement mortar. Further, it seems that the production of the amorphous phase reduces the speed of the hydration reaction in the cement kneaded product, thereby restraining the decrease in the strength of the cured body that is caused by the rapid hydration reaction.
Here, in view of the surface activity of the alumina cement, the larger the specific surface area of the alumina cement is, the higher the surface activity will be. Therefore, it is not necessarily desirable that the specific surface area of the alumina cement exceeds 5000 cm2/g.